1. Field of the Invention
The present invention relates to a high brightness light emitting diode and a method for producing the same, in which gallium phosphide is provided as a window and more particularly, the bonding process are applied twice.
2. Related Prior Art
For manufacturing light emitting diodes, it""s very important to promote brightness. Gallium phosphide (GaP) is a material with good electrical conductivity and high transparency in wavelength ranging from red to green, and therefore frequently applied to light emitting diodes (LEDs).
FIG. 8 shows a conventional LED structure including GaP. In this structure, a SiO2 layer 82, a reflective metal layer 83, a GaP layer 84, an active layer 85 and a gallium arsenide (GaAs) window 86 are sequentially presented on the silicon substrate 81. The electrodes 87, 88 are respectively formed on the GaAs window 86 and below the silicon substrate 81. The GaP material is provided here, but unfortunately doesn""t contribute to brightness of the LED.
U.S. Pat. No. 5,869,849 provides another LED structure and method for producing the same, in which the GaAs substrate can be removed once a GaP layer is epitaxed on the active layer of aluminum gallium indium phosphide (AlGaInP). Next, the epitaxial structure is directly bonded to a GaP substrate, and two electrodes are respectively formed on the GaP epitaxial layer and below the GaP substrate. According to such a structure, the GaP window may theoretically enhance brightness of the LED. However, lattice alignment is difficult and bonding directly to the epitaxial layer at high temperature will seriously decrease production yield.
Therefore, it is necessary to find a method for producing LEDs with GaP windows, so that the above disadvantages can be meliorated.
The object of the present invention is to provide a high brightness light emitting diode (LED) and a method for producing the same, so that production yield can be promoted.
The method of the present invention includes steps of: a) providing a temporary substrate for epitaxing; b) sequentially epitaxing an n-type cladding layer, an active layer with quantum well structure and a p-type cladding layer on the temporary substrate; c) forming an p-GaP layer on the p-type cladding layer; d) forming a metal contact layer on the p-GaP layer; e) etching a part of the metal contact layer, the p-GaP layer, the p-type cladding layer and the active layer, and an upper part of the n-type cladding layer to expose the n-type cladding layer; f) forming a p-type ohmic contact electrode and an n-type ohmic contact electrode on the metal contact layer and the exposed n-type cladding layer to complete a main structure of the light emitting diode; g) bonding the surface with the electrodes of the main structure to a glass substrate; h) removing the temporary substrate; i) forming a reflective mirror on a bottom surface of the n-type cladding layer; j) bonding a permanent substrate to a bottom surface of the reflective mirror; and k) removing the glass substrate.
The temporary substrate used in the present invention is not restricted, for example, a GaAs substrate. The active layer can be made from III-V or II-VI compounds, for example, AlGaInP, gallium nitride (GaN) and zinc selenide (ZnSe).
The technology applied in step b) can be any appropriate deposit methods, wherein MOVPE is preferred. The glass substrate bonded to the main structure of the LED can be previously coated with proper adherent material such as epoxy or wax. The temporary substrate is usually removed by etching or chemical mechanical polishing.
The reflective mirror can be formed by plating a reflective material, for example, In, Sn, Al, Au, Pt, Pd, Zn, Ag, Ge, Ni, Au/Zn, Au/Be, Au/Ge, Au/Ge/Ni, or mixtures thereof, or composites of high dielectric/low dielectric or dielectric/metal.
The permanent substrate of the present invention can be a silicon substrate or a metal substrate with good heat dissipation. Between the permanent substrate and the reflective mirror, an adhesive layer is involved, which can be a pure metal or an alloy with a melting point below 350xc2x0 C., or an organic adhesive with good heat dissipation and low operation temperature.
Between the metal contact layer and the p-type ohmic contact electrode, a transparent conductive film such as ITO (indium tin oxide) can be further added. Alternatively, the transparent conductive film can serve as the p-type ohmic contact electrode with a whole contact surface.
According to the above method, an LED composed of a GaP window and a reflective mirror with excellent reflectivity will be completed. Furthermore, brightness and yield of the LED of the present invention are promoted.